Chlorinated polyvinyl chloride (CPVC) is known to have excellent high temperature performance characteristics, among other desirable physical properties. Typically, CPVC has an excess of 57% bound chlorine. CPVC is conveniently made by the chlorination of polyvinyl chloride (PVC) by any one of several available methods including a solution process, a fluidized bed process, a photo-slurry process, a thermal process or a liquid chlorine process. Examples of these processes can be found in U.S. Pat. Nos. 2,996,489; 3,100,762; 4,412,898; 3,532,612; 3,506,637;3,534,013; 3,591,571; 4,049,517; 4,350,798; and 4,377,459.
CPVC is an important specialty polymer due to its high glass transition temperature, high heat deflection temperature, outstanding flame and smoke properties and chemical inertness. The glass transition temperature of the CPVC generally increases as the amount of chlorine increases. It is also known that CPVC resins have low impact properties. However, as the chlorine content increases, the CPVC becomes more difficult to process and becomes more brittle.
The increased demand for CPVC pipe, vessels, valves, fitting and other articles has provided a significant incentive to develop a better impact modified CPVC having increased heat deflection temperatures which have an increased ease of processing. Most of the efforts have been channeled to rigid CPVC applications where acceptable impact strength and dimensional stability under heat are critical. These include the manufacture of exterior structural products, rigid planes, pipes, conduits, injection molded and various other containers.
European Patent Application 0343545A2 to Lawson discloses a composition of crosslinked CPVC which has good melt strength yet improved processing properties such as reduced melt temperatures as well as reduced torque processing characteristics. However, in Table II, Recipe 1, Lawson also discloses a CPVC compound comprising a blend of CPVC resin formed by the use of a photo-slurry process having an inherent viscosity of 1.1 and 68.5% chlorine which is not crosslinked, an acrylic impact modifier and chlorinated polyethylene. In addition, European Patent Application 0603753 A1 to Hartitz dicloses a CPVC compound intended for low shear extrusion. The compound comprises CPVC resin having from 69% to 74% by weight chlorine; an acrylic impact modifier, a first chlorinated polyethylene containing from 32 to 37% by weight of chlorine and a Mooney viscosity of from 25 to 45, and a second chlorinated polyethylene containing from 36 to 42% chlorine and a Mooney viscosity of from 60 to 95. Compression molded plaques derived from compound exhibit a good balance of tensile strength, tensile modulus, Izod impact strength, heat deflection temperature and dynamic thermal stability.
U.S. patent application Ser. No. 08/565,910, filed Dec. 1, 1995 by Forsyth, et.al., discloses plastic pipe, fittings and other piping appurtenances which are prepared from CPVC formulations and meet the requirements of ASTM D 1784, cell class 23448-B. The CPVC resin used in these formulations has a specified weight percent of chlorine of at least 70%. The formulation includes impact modifiers, and other optional ingredients.
European Patent Application EP 0695782 A1 discloses a CPVC compound comprising a blend of a CPVC and an impact modifier containing a polyorganosiloxane. In Table 1, Compound #3, a CPVC resin containing 72% chlorine is used in conjunction with an impact modifier containing a polyorganosiloxane.
Although these various compounds exist, there still exists a need for a CPVC composition which has a high heat deflection temperature as well as good physical properties, chemical resistance and can be easily processed.
ASTM D 1784 sets forth the standard specifications for rigid CPVC compositions for general purpose use in extruded or molded form. In addition to the CPVC resin, the compound may include lubricants, stabilizers, non-poly(vinyl chloride) resin modifiers, pigments and inorganic fillers. The standard specifications are identified in terms of cell classifications, which are indicative of certain physical properties of the formulations. Cell Class 23447 identifies certain commercially available CPVC compounds. The first digit (2) identifies the base resin as CPVC. The second (3) and third (4) digits identify impact strength and tensile strength characteristics. The fourth (4) and fifth digits (7) identify the modulus of elasticity and the heat deflection temperatures.
______________________________________ Property and Unit Cell Limit ______________________________________ 2 Base Resin CPVC 3 Impact Strength (Izod), J/m 80.1 ft.lb./in. 1.5 4 Tensile Strength, MPa 48.3 psi. 7,000 4 Modulus of Elasticity, MPa 2482 psi. 360,000 7 Heat Deflection Temperature, .degree. C. 100 .degree. F. 212 ______________________________________
It is desirable to increase the heat deflection temperature to levels greater than 212.degree. F. However, by doing so, a general degradation is seen in one or more of the physical properties of the article made from such a compound. For example, simply increasing the chlorine content of the compound degrades impact strength levels below those mandated by ASTM D 1784. Adding or changing impact modifiers to compensate can degrade tensile strength and modulus of elasticity. Moreover, even if all the physical properties are maintained, the processability of the CPVC compound is at issue. A compound cannot degrade while being processed.
Dynamic thermal stability (DTS) is a measure of the processability of the CPVC compound. DTS is designed to measure the time-torque relationship of a particular formulation at a selected temperature using a Brabender Plasti-corder or a Haake Rheocord 90 or the like. The test value used for comparison is DTS time. Unless specified otherwise, DTS time is defined as time at a particular temperature and rotor speed, herein 21.degree. C./35 rpm, required for the instrument torque to fall to minimum value with the polymer compound in the molten state, before beginning to increase, presumably due to instability and accompanied by autogenous crosslinking.
Thus, there currently exists a need for a CPVC composition having a balance of good physical properties, and chemical resistance, which can be easily processed. In particular, a need exists for a CPVC compound which at a minimum meets the cell class 23447 of ASTM D 1784 which is easy to process. More particularly, there exits a need for a CPVC composition which has at a minimum a heat deflection temperature above 212.degree. F. and has a balance of physical properties as well as chemical resistance.